Consensus is all, and language can only ever evolve with respect of the collective, the culture of which is always evolving in and off itself, regardless of whatever absolutes & shibboleths we might set up along the way. These will pass away, as all things must in due course.
Very true, but you're not going to get a consensus when it comes to solecisms like 'should of', 'aks', 'pacifically'. We may be a social animal, but our societies are stratified. The demotic may spread (witness the Queen's English shifting from strict RP to estuarine since her accession) but it is hard to shift the basic building blocks which ar laid down and passed on by the 'ruling classes' for want of a better phrase.
So pronunciation changes are common - apart from Her Maj, there's the adoption of the rising terminal by British youngsters; whether from Aussie soaps or not I don't know - but changes in syntax and grammar are less common/
Writing and, more importantly, printing, have served to set 50,000 years of mutable, orally-transmitted language into a more rigid form. We are taught to write a certain way and, however laissez-faire the education system, that way is Standard English. Thus SE becomes the lingua franca, and those who don't speak and, more importantly, write SE, appear ignorant.